Plague

Plague is another infection that can strike humans and animals. It is caused by the bacteria Yersinia pestis, which has been the cause of three great human pandemics in the sixth, 14th, and 20th centuries. Throughout history, the oriental rat flea has been largely responsible for spreading bubonic plague. After the flea bites an infected animal, the organisms can multiply inside the flea. When an infected flea attempts to bite again, it vomits clotted blood and bacteria into the victim's bloodstream and passes the infection on to the next victim, whether small mammal (usually rodent) or human.

Although the largest outbreaks of plague have been associated with the rat flea, all fleas should be considered dangerous in areas where plague may be found. The most important vector (a vector is an animal that can transmit the disease) in the United States is the most prevalent flea of rock squirrels and California ground squirrels. The black rat has been most responsible worldwide for the continuing spread of plague in urban epidemics.

Signs and Symptoms

People infected with plague may suddenly develop high a fever, painful lymph nodes, and have bacteria in their blood. Some victims with the bubonic form of the disease may develop secondary pneumonic plague (a disease similar to pneumonia). Plague is contagious, and when the victim coughs, plague can spread. Pneumonic plague is the most severe form of the disease and if untreated, most people die.

As few as one to 10 organisms are enough to infect humans or other animals including rodents. During the early phase, the germs usually spread to lymph nodes near the bite, where swelling occurs. The infection then spreads to other organs such as the spleen, liver, lungs, skin, mucous membranes, and later, the brain.

In the United States, most victims with human plague have the bubonic form. If the organisms were used as a biological warfare agent, it most likely would be spread through the air and inhaled by victims. The result would be primary pneumonic plague (epidemic pneumonia). If fleas were used as carriers of disease, bubonic or septicemic (blood infection) plague would result.

Bubonic plague: Swollen lymph nodes (called buboes) develop one to eight days after exposure. Their appearance is associated with the onset of sudden fever, chills, and headache, which often are followed by nausea and vomiting several hours later. The buboes become visible within 24 hours and cause severe pain. Untreated, septicemia (blood poisoning) develops in two to six days. Up to 15% of bubonic plague victims develop secondary pneumonic plague and thus can spread illness from person to person by coughing.

Septicemia plague: Septicemia plague may occur with bubonic plague. The signs and symptoms of primary septicemic plague include fever, chills, nausea, vomiting, and diarrhea. Later, bleeding in the skin may develop, hands and feet may lose circulation, and tissue may die.

Pneumonic plague: Pneumonic plague may occur primarily from inhaling organisms in the air or from exposure to infected blood. Victims typically have a productive cough with blood-tinged sputum within 24 hours of symptom onset.

Diagnosis

The diagnosis of bubonic plague may be made if the victim has painful lymph glands and other common symptoms, especially if the victim has been exposed to rodents or fleas. But if the victim is not in an area where plague is present and symptoms are typical of other illnesses, the diagnosis may be difficult.

The doctor may view under a microscope a sample of sputum from a productive cough or the fluid from a swollen lymph gland.

Samples may grow in the laboratory and indicate plague within 48 hours and blood tests may also be performed.

Treatment

Victims of suspected plague will be isolated for the first 48 hours after treatment begins. If pneumonic plague is present, isolation may last for four more days. Since 1948, streptomycin has been the treatment of choice for plague but other antibiotics may be given.

If treated with antibiotics, buboes typically become smaller in 10-14 days and do not require drainage. Victims are unlikely to survive primary pneumonic plague if antibiotic therapy is not begun within 18 hours of the beginning of symptoms. Without treatment, 60% of people with bubonic plague die, and 100% with pneumonic and septicemic forms die.

Prevention

Fleas always must be targeted for destruction before the rodents, because killing rodents may release into the environment massive amounts of infected fleas, which will be hungry for a blood meal and, in the absence of rodents, the fleas will seek out any warm-blooded animal, including humans and infect them. Pesticides have been successful in getting rid of rats and other animal hosts. Public education about how plague spreads is an important part of prevention.

People who have been exposed to pneumonic plague and those who have been exposed to organisms in the air may be treated with antibiotics. Currently recommended antibiotics are streptomycin or gentamycin IM for 10 days, or until two days after the fever subsides. Alternative medications include doxycycline, ciprofloxacin, and chloramphenicol.

Contacts with victims who have bubonic plague do not need preventive medication. But people who were in the same environment as those who are infected may need preventive antibiotics. A previously FDA-approved plague vaccine is no longer manufactured. It was useful against the bubonic form of plague but not the more serious pneumonic (lung) form of plague, which is the kind most often expected in a terrorist incident. A new vaccine effective against all varieties of plague is under development.